a children's guide to python...

A children's guide to

Python programming

By Simon Haughton

(Tested on Python 3.0 for iOS.)

www.simonhaughton.co.uk 2

1. Printing text and creating variables

� Open the Python app and tap .

Press and start a program.

Type a name for your program and select a folder to save it in.

� Type these commands into the 'script' window:

� Press and start a program.


� Type these commands in and then them:

Press and watch

the 'interpreter' window.

print("Hello world.")

print("\n")

print("I am learning Python.")

What does the print command do?

What does printing \n do?

What happens if you make a mistake in

your commands?

Program - A sequence of

commands that are followed

in order to carry out a task.

Run - Carrying out the

commands in a program. Also

known as execute.

forename = input("What is your forename? ")

print("Hello",forename)

What does the input

command do?

Does it matter if you type

in text other than your

name? Variable – A value that can be

stored and used in a program.

• Add a variable to store a surname. Then add a print

command so it prints their full name.

Edit and

improve:

print("Hi",forename,surname,"!")


2. Calculations and random numbers

� Open the Python app and tap .

Press and start a program.



� Press and start a program.



print(100+10) Is the calculation still solved if

you use a negative number or

a decimal number?

• Change the commands to do a different calculation,

such as a: take away -, multiplication * or division /.

Edit and

improve:

Testing - Trying out a program to check if it works as expected.

Debugging - Finding and correcting mistakes in a program's source code.

import random

number = random.randrange(10,20,1)

print(number)

What does the .randrange

command do?

• Change the number 10 to a smaller number and the

number 20 to a bigger number to see what effect

this has on the program.

• Add some commands to do calculations with the

random number. e.g.

Edit and

improve:

print(number+10)


3. Number variables and adding comments

� Open the Python app and start a program.

Type these commands in and then them:

� Add these commands to your program:

number = int(input("Type a whole number: "))

answer = number * 8

print(number,"multiplied by 8 is",answer)

What happens if you type in a decimal number

instead of an integer (whole number)?

• Find out what changing int to float lets you do.

(Remember to change it back to int afterwards!)

• Add commands so the answer to an addition is

printed as well. You will need to use another variable

called answer2:

• Change the program so you have to type in two

numbers at the start to use in each calculation. You

will need to use another variable called number2.

Remember to print it on the screen before you show

the answer!

Edit and

improve:

# This is a comment.

Comments - Notes in a program's code which explain

what commands do to remind you. They are not run.

Does text on a line starting with a hash then a

space (# ) do anything when the program is run?

• Type some comments beside some commands to

explain what they do.

Edit and

improve:

answer2 = number + 6

print(number,"add 6 is",answer2)


4. If statements



� Start a program.


answer = input("Do cats bark? ")

if answer = = "no":

print("Correct")

else:

print("Wrong")

IF statement - Decides which commands to run depending

on whether certain things (conditions) are true or false.

What does this program do?

Why do you think two equals

signs are used and not just one?

mark = int(input("Score: "))

if mark > 80:

print("Outstanding")

elif mark > 40:

print("Great")

else:

print("Good")

• Change the question being asked (and the answer

too, if needed).

Edit and

improve:


What does the elif command

let you do?

• Add another elif command in the middle so that a

score of more than 60 is rated as "Super".

Edit and

improve:

Create a program that asks a maths calculation and

prints if the user answers it right or wrong. Can you

change one of the numbers in it to a random number?

Programming challenge:


5. Lists



� Start a program, type these commands in and then them:

import random

colours = ["red","green"]

animals = ["lions","bears"]

print("My rainbow zoo has:")

colour = random.choice(colours)

animal = random.choice(animals)

print(colour,animal)

colour = random.choice(colours)

animal = random.choice(animals)

print(colour,animal)

Use copy and paste to help

you quickly copy this!


What are the purposes of

the lists?

List - A set of values.

• Put more items in the list to make the rainbow zoo more fun! Edit and

improve:

vehicles = ["bus","car","train"]

print(vehicles[0])

print(vehicles[1])

print(vehicles[2])

vehicles.append("plane")

print(vehicles)

vehicles.pop(2)

vehicles.insert(2,"boat")

print(vehicles)

vehicles.remove("car")

print(vehicles)

Can you see what the:

.append, .pop,

.insert and .remove

commands do?

Create a list to store some names. Add commands to: .append, .pop,

.insert and .remove names. Find out what the .sort() command does.



6. Functions



import random

def cointoss():

options = ["heads","tails"]

result = random.choice(options)

print(result)

cointoss()

cointoss()

cointoss()

cointoss()

cointoss()


Why is better to call the

function five times than to

copy all of its commands five

times?

Function - A sub-program which

is placed at the start of a bigger

program and can be called (run)

later using its name.

• Change the program so it shows the results of rolling

a six-sided dice instead. You don't need to put ""

around the options because they are numbers.

Edit and

improve:

Create a program that tells a user's fortune by calling (running) a

function two times which randomly picks a prediction from a list:

e.g. You will be given money.

You will become famous.

You will see an alien.

You will find a lost item.

You will score well in a test.

Can you ask the user to input their name so that it is included in the

predictions (e.g. Tom will be given money)?



7. Iteration (looping)





for i in range(4):

print("Hello world")

What happens if you change

4 to a different number?

Iteration - A way of repeating or looping commands multiple times.

for i in range(1,10):

print(i*10)

What happens if you change 1

and 10 to different numbers?

If = = means 'equal to',

what does != mean?

What does a while loop do?

password = "fish"

guess = ""

while (password != guess):

guess = input("Enter password: ")

if password = = guess:

print("Correct")

else:

print("Try again")


Create a program in which the computer sets the password as a random

integer from 1 to 100 and user has to correctly guess it.

Can you use: if, elif and else commands to give the user clues (e.g. "Too

high" or "Too low")? Can you add a variable which counts the number of

guesses (count = count + 1)?


8. Parameters and validation




def spell(word):

for i in range(0,len(word)):

print(word[i])

spell("said")

spell("because")

Parameter - A way of passing a

value from the main program to a

function when it is called (run).

Validation - Automatic checking by a computer to ensure that an entered value is sensible.

What is the

purpose of this

function?

How could it

be useful?

Create a function that prints the biggest of two values, passed to it in parameters.

The user will input the two integers they want to compare using the validation function.


• Insert the len(word)command to make the function print how

many letters are in the word as well.

• Change the program so you can type any word in to get passed to the

function.

• Insert the ord(word[i]) command to the iteration so the special

Unicode number of each letter is printed as the word is spelled out.

Edit and

improve:

Create a function that uses the chr(integer) command to convert a Unicode

integer you type in into a letter. You could use this to decipher a secret code made

from Unicode numbers (possibly having to add/subtract another number first as well)!


def validation():

number = 0

while True:

try:

number = int(input("Type a whole number: "))

except ValueError:

print("Not a whole number!")

else:

return(number)

x = validation()


9. Algorithms

Create a simple version of a Snakes and Ladders game:

• Can you add more print commands to display what is happening on screen?

• Can you make the game print the player's name at the end?

• Can you add another player to the game whose position is stored in a variable

called position2? You will need to make the game let each player move in

turns. You could create a variable called finished which is set to 0 at the

start and changes to 1 when a player wins, forcing the game to stop.


Algorithm - An explanation of a the processes or instructions a program carries

out, usually described in a flowchart.

Many thanks to Paul Meakin and Phil Bagge for the inspiration to learn Python and write this guide!

www.code-it.co.uk/philbagge.html

Set position = 0

Is position

> 100?

Run move function

Print a "Well

done" message

Start

Stop

yes

no

Press the

keyboard to roll

Start

no

Set dicenumber as a

random number

between 1 and 6.

position =

position +

dicenumber

Is position

on a snake or

ladder number?

Stop

Change the position so

it is more or less (use: if,

elif and else)

yes

move function

Main program

a children's guide to python...

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